GX1 is a raster graphics format associated with the Show Partner presentation software for MS-DOS, and supported by the Microsoft Paintbrush graphics editor. It is unclear whether there is just one GX1 format, or perhaps two unrelated formats.
See also GX2.
At least some GX1 files begin with
- https://telparia.com/fileFormatSamples/image/gx1/ → *.gx1
- Microsoft Paintbrush 2.0, from Daniel's Legacy Computer Collections – Note the screenshot showing "GX1" on the menu.
- ftp://ftp.oldskool.org/pub/misc/Software/Graphics/Presentation/Show%20Partner%20FX/ ...